1. Field of the Invention
The present invention relates to material and members suitable for making apparatus in which are used, stored, or conveyed, alcohol fuels or alcohol-mixed petroleum fuels herein generically called alcoholic fuels including these fuels and organic fuels such as ethers, particularly for pumps, nozzles, valves and other members having to striking or sliding members in electronic fuel injection systems of internal combustion engines.
2. Description of Related Art
Petroleum fuels such as gasoline and light oil have been used in internal combustion engines for automobiles, and in the case of internal combustion engines in which these fuels are used, electronic fuel injection systems controlled by computers are used for cleaner exhaust gases, improvement in power and performance, and reduction of fuel expenses to bring good results. In electronic fuel injection systems, a heat treated SUS440C (corres. to AISI440C) steel specified in JIS which is superior in wear resistance is used for a valve portion (electronic fuel injection nozzle) for supply and control of fuels, and the valve portion is generally used without need for replacement before the car is scrapped.
As the fuels of internal combustion engines for automobiles, use of alcoholic fuels in place of petroleum fuels has been investigated for the reasons of recent circumstances relating to petroleum (increase of petroleum availability costs and reduction in production) and for diminishing exhaust gases (NOx), and some alcoholic fuels have been subjected to practical tests.
Use of methyl alcohol, ethyl alcohol, methyl-tert-butyl ether and the like has been examined as alcoholic fuels.
These alcoholic fuels are inferior in lubricity to petroleum fuels and there are the problems of occurrence of abrasion and peeling of materials of rotors in fuel pumps and sliding parts or parts subjected to striking-type contact in fuel injection nozzles, and also and the problem of corrosion of fuel systems caused by water contained in alcoholic fuels, oxides of alcohols (acetaldehyde, formaldehyde), and impurities in alcoholic fuels (acetic acid, formic acid).
As materials for members of devices in which alcoholic fuels are used, Japanese Patent Kokoku (Post-Exam. Publication) Nos. Hei 1-15585 and 1-15584 and Japanese Patent Kokai (Laid-Open) No. Sho 62-93347 have proposed Fe-based sintered alloys having both abrasion resistance and corrosion resistance for fuel pumps which are steels containing Nb as an essential component, steels containing at least one of P and B and at least one of Ti and Zr as essential components, and steels containing only C and Ni as additive elements, respectively. Furthermore, Japanese Patent Kokai (Laid-Open) No. Sho 61-6260 has proposed steel sheets for fuel tanks, but abrasion resistance and peel resistance have not been considered.
In the development of materials for members of devices in which alcoholic fuels are used, the inventors have conducted a working test where a closed circuit of a fuel tank, a fuel pump and an electronic fuel injection nozzle is used an alcoholic fuel is circulated to operate the electronic fuel injection nozzle, and an investigation of the valve portion of, the nozzle in an alcohol fuel engine is made after the valve portion is subjected to a practical test. As a result, the inventors have confirmed that deterioration of the valve in shielding properties readily occurs when the injection nozzle is made of conventional SUS440C steel.
The part having deteriorated shielding properties was microscopically examined. As a result, it has been found that corrosion wear and peeling owing to striking contact occurred in the surface portion of the nozzle (which wear and peeling are called "fretting abrasion" or "fretting fatigue") as shown in FIG. 4 and this is a cause for deterioration of the shielding or protective qualities of the material.